血吸虫病炎症微环境对肝实质细胞转归的影响及其在肝纤维化中的作用

Hepatic fibrosis, as a serious pathology of schistosomiasis, may lead to the death of patients in advanced stage. Effective therapy or preventive measures for hepatic fibrosis remains unsolved. Hepatic fibrosis has been identified as a kind of pathological repair arising from excessive deposition of ECM in liver launched by activated hepatic stellate cells, but recent studies have showed that parenchymal liver cells also participate in this process. However, liver cells-based healing associated with liver fibrosis caused by schistosome is poorly elucidated. The differentiation of hepatic-associated progenitor cells into hepatocytes may be pivotal in wound repair of liver. There are many factors were involved in the wound repair associated with progenitor cells, including the functional status of hepatic progenitor cells, efficiency of trans-differentiation, the microenvironment of hepatic inflammation, and the relevant regulatory signaling pathways such as Hippo, Wnt and Notch. Our previous studies have shown that Wnt signal-related molecules in hepatocytes were elevated after S. japonicum infection. The liver fibrosis became alleviated when Wnt signaling in liver was suppressed by Dkk1, and the liver fibrosis became exacerbated when exogenous Wnt3a was introduced into the liver. This project is administrated to study the role of hepatic progenitor cells in liver fibrosis of shcistosomiasis, and to reveal the effect of inflammatory microenvironment on trans-differentiation from hepatic cells to progenitor cells. Furthermore, we would like to evaluate the hepatic repair processes by improving the trans-differentiation of progenitor cells through the regulation of Hippo, Wnt and North in genetically modified mice. Thereby, this research will extend our understanding on pathology of schistosomiasis and explore a potential target to gene therapies for hepatic fibrosis in relevant liver diseases.

肝纤维化是血吸虫病最重要的病理改变，目前尚无有效的治疗方法。肝纤维化是由于肝星状细胞激活导致纤维组织过度沉积的一种病理性修复，有研究表明，肝实质细胞也参与了纤维化病变，但在血吸虫病肝纤维化中的作用尚未见未报道。在肝脏修复中，具有多向分化潜能的肝祖细胞分化为肝实质细胞起着重要作用，影响其修复的主要因素有肝祖细胞的功能状态、残留肝细胞向肝祖细胞转化的效能、局部微环境及增殖分化相关的Hippo、Wnt和Notch信号等。我们的前期研究发现，肝实质细胞的Wnt分子在血吸虫感染后高表达，抑制Wnt能改善肝纤维化。本项目拟研究肝祖细胞在血吸虫病肝纤维化过程中的作用；并通过基因修饰小鼠，明确炎症微环境是否通过Hippo、Wnt和Notch信号对肝实质细胞向肝祖细胞转化产生影响，进而通过提高肝祖细胞的转化判断其对肝纤维化进程的影响，为深入阐述血吸虫病肝纤维化的机制和治疗提供理论基础和新的靶点。

HSC的激活并分化成为成纤维细胞是肝纤维化形成初始的中心环节。目前对血吸虫病肝纤维化的研究主要集中在HSC的激活及其信号传递上，本项目更多集中在研究肝细胞、HSC以及肝枯否细胞共同对血吸虫感染导致慢性肝损伤和肝纤维化的作用机制上。我们的研究揭示了肝细胞自身的Wnt信号通路能直接和间接促进肝星状细胞增殖活化，且与SOX-9的强烈高表达密切相关；Wnt下游的YAP蛋白 信号也参与了此调节过程。若抑制WNT，可在细胞水平明显抑制HSC的活化和促纤维化的改变，在动物水平则可显著改善小鼠感染后的肝纤维化。另外，血吸虫感染小鼠枯否细胞上清处理肝星状细胞的YAP、MST、CTGF、KI67等HIPPO通道相关分子均有变化，且αSMA、CTGF明显升高，说明血吸虫感染小鼠枯否细胞会促进肝星状细胞的活化和纤维化，且肝星状细胞受肝内枯否细胞的调控可能与HIPPO通道被抑制有关。相关免疫学研究发现，虽然用PD-L1抗体部分阻断了CD4+ T细胞的免疫负调控，但并未能改善肝纤维化，说明一旦炎症应答启动，纤维化进展并不受单纯免疫调控的影响。在本项目预期目标之外，我们还发现，促进AMPK的二甲双胍可通过促进HSC的线粒体自噬，纠正线粒体在细胞活化过程中的损伤而部分改善线粒体功能，从而抑制HSC的持续激活，进而改善血吸虫肝纤维化，其机制与TRAP1-PINK-Parkin有关，而与线粒体的氧化磷酸化可能无关。 总之，我们的研究全面揭示了血吸虫病导致的肝纤维化过程中肝细胞、肝间质细胞的相互影响以及细胞内主要信号通路机制，为开发这一系列肝损伤导致的肝纤维化提供了新的靶点。